The rate of urinary acidification by turtle bladder in vitro is coupled to the oxidation of glucose via the pentose phosphate shunt. Since the end product of the pentose shunt is NADPH, it is proposed that H ion transport is somehow coupled to the oxidation of NADPH. In this series of studies we will examine this dependency by determining the effect of changes in H ion transport for the redox state of pyridine nucleotides and ATP/ADP. Also we will examine the effect of known oxidants on the NADPH/NADP ratio and their subsequent effect on H ion and Na transport. Since we have demonstrated that the enzymes of the pentose shunt and carbonic anhydrase are present in greater activity in the mitochondria-rich cells of the turtle bladder, we will begin studies to determine if this cell type is the primary cell responsible for the acidification process.